Apparatus for molding hollow plastic products



Dec. 18, 1962 J. H. MILLER ETAL 1 APPARATUS FOR MOLDING HOLLOW PLASTICPRODUCTS 2 sheets-she t l Original Filed Sept. 20, 1957 INVf/VTUR %ORNEL 1962 J. H. MILLER ETAL 3,

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Original Filed Sept. 20, 1957 Unite Stmes atent Orifice attests PatentedDec. 18, 1962 33353518 APPARATU FOR MOLDING HOLLOW PLASTIC PRODUQITSJohn H. Miller, Hoil Wood, and Millard O. Helms, Sepulveda, Calif,assignors, by mesne assignments, to Moid-A-Rarna, Inc, Los Angeles,Calif., a corporation of California Original application Sept. 20, 1957,Ser. No. 685,261. lgliygged and this appiication Feb. 29, 19%, Ser. No.

8 Claims. (Cl. 1826) This invention relates to an apparatus for quicklyand accurately molding a quantity of hollow plastic products such asplastic figures, toys and the like.

The present application is a division of my copending application,Serial No. 685,261, filed September 20, 1957, and now abandoned.

One of the principal objects of the present invention is to provide amachine capabe of producing hollow plastic products in rapid succession.Another object is to provide a machine having aplurality ofcomplementary mold sections which sequentially engage and disengage eachother, a hollow plastic product being automatically formed during thecycle of operation when the mold sections are in mutual engagement. Inthis connection, it is a specific object to provide an apparatus whereina molten plastic material is forced, under pressure, through the moldcavity and is then followed by a blast of compressed gas which forcesthe core of molten plastic from the cavity leaving a wall of solidifiedplastic against the mold surfaces. A still further object is to providean apparatus which may be easily adapted for molding large quantities ofplastic products of different size and shape.

Other objects will appear from the specification and drawings in which:

FIGURE 1 is a broken front elevation of an apparatus embodying thepresent invention; FIGURE 2 is a broken top plan view showing structuraldetaifs of the apparatus; FIGURE 3 is an enlarged front elevation oftheapparatus shown partly in section and taken along line 3-3 of FIGURE 2;FIGURE 4 is a ver'ical sectional view of the valve assembly similar tothe valve assembly shown in FIGURE 3 but illustrating the valve memberin a different position; and FIGURE 5 is a vertical sectional view takenalong line 55 of FIGURE 2.

Referring to the embodiment of the invention illustrated in FIGURE 1 ofthe drawings, the numeral generally designates a frame having supportlegs 11 and a generally horizontal platform 12. Beneath the platform isa tank 13 which serves as a reservoir for a molten plastic material suchas liquid polyethylene. The interior of the tank is lined with a spiralsteam conduit 14 for maintaining the plastic material in a molten state.The steam jacket or conduit may be connected to any suitable source ofsteam (not shown).

Beneath platform 12- and within the confines of tank 13 there is a valveassembly generally designated by the numeral 15. This assemblyessentially comprises a valve casing 16 and a movable valve member 17.It will be noted that the valve assembly is supported from the platformwell above the level of molten plastic material within tank 13. A pump1.8 powered by motor 19 drives molten plastic material from thereservoir to the valve assembly through conduit 29. Both the pump andthe motor may be immersed within the mass of molten plastic and as shownin FIGURE 1 the motor may be operated by compressed air or other fluidcarried by pipes 21 and 22. If desired, a bleed conduit 23, equippedwith an adjustable valve 24 may be interposed between the pump and thevalve assembly and along conduit 29 for regulating the flow of plasticmaterialto assembly 15.

In the illustration given a pair of mold sections 25 and 26 are movablysupported upon the upper surface of platform 12 above tank 13. Clampingassemblies 27 and 28 connect the respective mold sections to horizontalpiston shafts 29 and 30. These shafts extend through cylinders 31 and 32respectively.

As shown in FIGURE 3, cylinder 31. has a cylindrical side wall 33 and apair of end plates 34 and 35 secured thereto by means of bolts 36. Theouter end plate 34- is welded or otherwise secured to a horizontal shaft37 which extends in a direction transverse to the axis of the pistonshaft 29. Opposite end portions of the transverse shaft extend throughvertical mounting plates or members 38 and 39 disposed on opposite sidesof the cylinder. The parallel plates 38 and 39 may be welded uponplatform 12 or may be rigidly secured thereto in any other suitablemanner.

Since the transverse shaft is slidably received by plates 38 and 39,lateral adjustment of the piston cylinder and shaft may be accomplishedby shifting the position of shaft 37 with reference to the mountingplates. As shown most clearly in FIGURE 5, shaft 37 is equipped with adepending arm 40 which has a threaded horizontal bore adapted tothreadedly receive adjustment screw 41. One end of the adjustment screwprojects through an opening in plate 38 and is freely rotatable therein.However, the enlarged end 42 of the screw restricts its longitudinalmovement relative to the mounting plate. Therefore, upon rotation of theadjustment screw, the piston cylinder 31 and shaft 29 are shiftedlaterally between the vertical mounting plates.

In FIGURE 3 it will be seen that shaft 29 is equipped with a piston 43which slidably engages the inner surface of cylinder wall 33. Ascompressed air or other fluid flows into the outer portion of thecylindrical chamber from conduit 44 (FIGURE 1), piston 43 is fo'cedinwardly along with shaft 29 and mold section 25, and the mold sectionis moved into a first position directly above valve assembly 15 (FIGURE3). On the other hand, when the compressed air is forced into the oppo-.Site end of the cylinder through conduit 45 the movable mold section isshifted to a second or retracted position (FIGURES 1 and 2).

Like piston cylinder 31, cylinder 32 is provided with a transverse shaft46 slidably carried by mounting plates 47 and 43. Adjustment means 49 isidentical in structure and operation to the depending arm 40 andthreaded screw 41 which had been previously described. Since thestructure and operation of the opposing piston assemblies are identical,a more detailed description of the structure of cylinder 32 is believedunnecessary herein. When compressed air passes through conduit 50 intothe outer end portion of cylinder 32, a shaft 30 moves inwardly andcarries mold section 26 into a first position above the valve assembly.Mold section 26 is returned to its original or second position when airis forced into the opposite end of the cylinder through hose 51. Hence,the two piston assemblies work in opposition, the two mold sections 25and 26 having their opposing vertical surfaces in contact with eachother when each of the sections is in its first position, and beingspaced from each other, as shown in FIGURE 1, when each of the sectionsis in its second or retracted position.

Referring to FIGURE 1 the paired air supply conduits for each pistoncylinder are connected to solenoidoperated valves 52 and 53respectively. The solenoid valves are in turn connected by pipes 54 to amanifold 55 which extends from a suitable source of compressed 3 air orother pressure fluid (not shown). If desired, manifold 55 may beprovided with a shut-off valve 56.

In the illustration given the mold support structures 27 and 28 areadjustable to accommodate mold sections of various sizes. The twosupport structures are identical and are each provided with a horizontalbar 57, 58, respectively, which extends transversely with reference tothe direction of movement of the mold sections. The mold sections areheld in place against these bars by longitudinally extending clampingmembers 59 (FIGURE 2) which are adjustably secured to the bars byvertical bolts 6a) and which are equipped with set screws 61 forengaging the mold sections and maintaining them in opposing relation.

As illustrated most clearly in FIGURE 3, the opposing surfaces of themold sections have complementary recesses which together define a cavity62, when the opposing surfaces are in contiguous relation. Cavity 62 iscompletely closed except for lower inlet and outlet openings provided byone or both of the mold sections which communicate with inflow andoutflow passages 63 and 64 provided in platform 12 and valve casing 16.While I have shown only a pair of such passages in the drawings, it willbe understood that a. greater number may be provided depending upon thesize and shape of the plastic product to be formed.

To maintain the mold sections at the reduced temperature required forproper solidification of a portion of the molten plastic materialpassing through cavity 62 during operation of the apparatus, I provideeach of the sections 25 and 26 with flow passages 65 and 66. Thesepassages or chambers are provided with inlet and outlet openings 67 and68 respectively, and a coolant such as cold water is carried into andout of these chambers by flexible hoses 69 and conduits 70, as shown inFIGURE 1. In this manner, coolant is circulated through the moldsections and the sections are maintained at a suitable and uniformtemperature.

Referring to' FIGURES 3 and 4, it will be observed that the valve casing16 has a cylindrical bore 71 extending therethrough and that the valvemember 17 is slidable between two positions within that bore. Valve 17is generally dumbbell shaped; that is, it has enlarged cylindrical endportions 72, 73 and an intermediate portion 74 of reduced diameter. Apair of openings 75 and 76 extend through the casing wall andcommunicate with bore 71 at diiferent points along its longitudinalextent. It will be noted that the length of intermediate portion 74 isat least as great as the distance between spaced openings 75 and 76. Thecasing wall about opening 75 is threaded for threadedly receiving theupper end portion of conduit 20, the lower portion of that conduit beingconnected to pump 18 within tank 13. If desired, the casing wall aboutopening 76 may be similarly threaded to receive fitting 77.

One of the end portions of the valve member, end portion 72, isthreadedly connected to a shaft 78 which is axially aligned with thevalve member and with bore 71. Shaft 78 is provided with a longitudinalflow passage 79 extending therethrough and this flowrpassage is indirect communication with a flow passage provided by the enlargedportion or head 72. As shown most clearly in piston 83 is fixed uponshaft 78 adjacent the opposite end thereof and this piston is disposedwithina cylinder 84 which is rigidly secured by bolts 85 or by any othersuitable means to the underside of platform 12. The piston isreciprocated within the cylinder by compressed air carried by conduits86 and 87 extending from solenoid valve 88. The solenoid valve is inturn connected to manifold 55 by pipe 89 (FIGURE 1).

At its outermost end, the tubular shaft 78 is connected by fitting 96 toone end of a flexible tube or hose '91. The other end of that hose isconnected to a solenoid-operated valve 92 attached to manifold 55.Hence, when valve 92 is in open position, compressed air may flow fromthe manifold through hose 92 and tubular shaft 78 to valve head 72. itwill be noted, therefore, that shaft 78 not only functions as a pistonshaft for reciprocating the slidable valve member 17 but also serves asa conduit for delivering compressed air to the vertical inflow passage63 and to the cavity defined by the complementary mold sectrons.

To prevent solidification of plastic material within the valve casing,we have provided the casing with a steam chamber or compartment 93 forthe circulation of steam through the casing and about bore 71. Pipes 94extend from the steam chamber of the valve casing (FIGURE 1) and may beconnected to the same conduits which carry steam to and from the heatingcoil lining the interior of tank 13-.

Referring to FIGURES l and 2, it will be seen that means are providedfor pushing plastic products formed by the mold sections oil of theplatform 12 where they may then be collected in any suitable receptacle(not shown). Such means comprises a piston assembly 95 which is disposedso that horizontal piston cylinder 96 is equidistant from the moldsections with its axis normal to the direction of movement of thosesections. Like the piston structures already described, piston assembly95 is operated by compressed air delivered through a pair of conduits 97and 98. A solenoid-operated valve 99 is disposed between these conduitsand a pipe 109 branching from manifold 55.. Valve 99 thereby controlsthe flow of air through the conduits leading to opposite ends of thepiston cylinder 96. The end of the piston shaft nearest the moldsections is equipped with an upstanding pusher plate or member 101 whichis retracted out of the path of movement of the mold sections whencompressed air flows to the front of the piston cylinder through conduit97. However, when valve 99 directs the compressed air through conduit98, the pusher member is driven forwardly between the spaced moldsections to sweep or push the plastic product formed by the molds oiT ofplatform 12 and into a suitable receptacle.

From the foregoing, it is believed apparent that the operation of theapparatus depends upon the flow of compressed air or other fluid to theseveral piston cylinders and that this air flow is in turn controlled bythe sodenoid valves associated with the respective piston assemblies. Atimer, diagrammatically illustrated in FIGURE 1 and designated bynumeral 182, is electrically connected through branched conduit 193 tothe solenoids of valves 52, 53, 88, 92 and 99 and controls thesequential operation of these electrically actuated valves. Since suchtimers are Well known in the art, a detailed description of itsconstruction and the electrical circuit involved in believed unnecessaryfor purposes of dis closing the present invention.

In the operation of the embodiment shown in the drawlugs and describedabove, pump 18 directs a continuous flow of molten plastic materialupwardly through pipe 20 and into the valve casing. The amount of moltenplastic flowing into the valve casing 16 through opening may be variedby manually adjusting the by-pass valve 24. When the valve member 17 isin the position shown 7 in FIGURES l, 2 and 3, the liquid plastic flowsinto the portion of the bore disposed between the ended portions orheads72 and 73 of the valve member and returns to tains the casing at asufiiciently high temperature to prevent solidification of the plasticmaterial.

At the commencement of each cycle of operation the movable parts of theapparatus are in the respective positions shown in FIGURE 1.Electrically operated valve 92 is closed, thereby preventing the flow ofcompressed air to valve assembly 15. Timer 162 first switches thesolenoids of valves 52 and 53 so that compressed air passes into theouter or remote ends of cylinders 31 and 32 and drives the mold sections25 and 26 into engagement directly above the valve assembly 15. Afterthe opposing surfaces of the mold sections are in contiguous relation(FIGURE 3), valve 88 is electrically actuated to permit the flow ofcompressed air through conduit 87 and into piston cylinder 84. Valve 17is thereby shifted into first position wherein end portion 73 seals offopening 76 and opening '75 is placed into direct communication withpassage 63 extending upwardly through the valve casing and platform 12(FIGURE 4). Since the flow of liquid plastic is no longer bypassedthrough opening 76 it passes upwardly through bore 71, passage 63 andinto the mold cavity 62. As soon as the molten plastic has completelyfilled the mold cavity, valve 88 is again electrically actuated toreverse the how of compressed air into cylinder 84 and to move the valvemember or body into the second position shown in FIGURE 3. At the sametime valve 92 is electrically opened, thereby permitting compressed airto flow through the tubular piston shaft 78 and through the alignedpassages of the valve member and valve casing. The blast of air passingupwardly through passage 63 drives the molten core of plastic materialwithin the mold cavity out through passage 64 and back into the tank 13,thereby leaving a layer of solidified plastic material against therelatively cool surfaces defining the mold cavity. Valve 92 then closesto interrupt the flow of air through the mold cavity and solenoid valves52 and 53 are electrically actuated to reverse the flow of compressedair to piston cylinders 31 and 32. After the mold sections have beenshifted into retracted positions the solenoid-controlled air-operatedpiston assembly 95 drives the pusher member 101 forwardly to sweep thehollow molded product off of the platform 12 and into a suitablereceptacle. When the pusher member has again returned to its originalposition, the operating cycle is completed. The above described stepsare then repeated to form any desired number of hollow plastic productsquickly and automatically.

As already pointed out, the mold support structures 27 and 28 areadjustable to accommodate mold sections of various dimensions.Therefore, it is apparent that larger (or smaller) mold sections may besubstituted for those shown in the drawing and that hollow plasticproducts of different sizes and shapes may be formed by the apparatus ofthe present invention. Cylinders 31 and 32 may be laterally repositionedby adjusting the screws 41 and 49 to insure proper alignment of passage63 and the inlet opening of the mold cavity when the mold sections arein contiguous relation.

While in the foregoing we have disclosed the present invention inconsiderable detail for the purpose of illustrating an embodimentthereof, it will be understood that many of these details may be variedconsiderably without departing from the spirit and scope of theinvention.

We claim:

1. In an apparatus for molding hollow products of a plastic capable ofmelting upon heating and of passing into a hardened state upon cooling,a pair of mold sections having opposing surfaces provided withcomplementary recesses together defining a cavity and having inlet andoutlet openings communicating with said cavity, means for cyclicallyshifting each of said mold sections between a first position whereinsaid opposing surfaces are in contiguous relation and a second positionwherein said surfaces are spaced apart, a valve casing having a passagecommunicating with said inlet opening when each of said mold sections isin said first position, a source of molten plastic material, a source ofcompressed air, passage means for conducting a continuous stream ofmolten plastic and a stream of compressed air from said sources to saidvalve casing, a valve member being movable between a first positionwherein said source of molten plastic communicates with said casingpassage and a second position wherein said source of compressed aircommunicates with said passage and said passage means returns saidcontinuous stream of molten plastic to its source, and means for movingsaid valve member from said first position to said second position whileeach of said mold sections is in first poistion, whereby, when saidsections are disposed with said opposing surfaces in contiguous relationmolten plastic material flows into said cavity and is followed by ablast of compressed air as said valve member moves from said first tosaid second position, said compressed air forcing the core of moltenplastic material in said cavity through said outlet opening to form ahollow plastic product, and means associated with said valve casing forcirculating molten plastic continuously through said passage means whensaid valve member is in both its first and its second positions.

2. An apparatus for molding hollow products of a plastic capable ofmelting upon heating and of passing into a hardened state upon coolingcomprising a frame providing a horizontal platform, a pair of moldsections movably mounted upon said platform for horizontal movement inopposite directions toward and away from each other, said sectionshaving opposing vertical surfaces provided with complementary recessesdefining a cavity when said sections are in contiguous relation andhaving inlet and outlet openings communicating with said cavity, meansfor cyclically moving each of said mold sections between a firstposition wherein said opposing surfaces are in contiguous relation and asecond position wherein said surfaces are spaced apart, a valve casingdisposed below said platform, said casing and said platform beingprovided with a flow passage communicating with the inlet opening ofsaid mold cavity when said sections are in first position, a source ofmolten plastic material, a source of compressed air, passage providingmeans for conducting compressed air and a continuous stream of moltenplastic from said sources to said valve casing, a valve member movablewithin said casing between a first position wherein said source ofmolten plastic communicates with said flow passage and a second positionwherein said source of compressed air communicates With said passage andwherein said passage-providing means returns molten plastic to itssource, means for moving said valve member from said first position tosaid second position while said mold sections are in contiguous relationand pumping means associated with said passage providing means forcontinuously circulating molten plastic through said apparatus.

3. The structure of claim 2 in which means are provided for pushingplastic products formed by said mold sections out of the path of thesame while said sections are spaced from each other.

4. In an apparatus having a pair of complementary mold sections formolding hollow products of a plastic capable of melting upon heating andof passing into a hardened state upon cooling, a valve assembly forcontrolling the flow of molten plastic and compressed air-to said moldsections, said valve assembly comprising a valve casing having a boretherethrough and a valve member movable within said bore between a firstand a second position, said casing providing a flow passage extendingfrom said bore towards said mold sections, said valve member having apassage therethrough aligned with the flow passage of said casing fordelivering compressed air to said mold sections only when said valvemember is in said second position, said casing also providing an spasmsinlet opening for the flow of molten plastic into said bore and a returnopening for the flow of plastic out of said bore and back to its source,said inlet opening communicating with said casing passage only when saidmovable valve member is in said first position, said valve memberblocking communication between said flow passage and said valve passagewhen said member is in its first posi tion and blocking communicationbetween said fiow passage and said inlet opening when said valve memberis in its second position, said inlet and return openings communicatingthrough said bore for the return of molten plastic when said valvemember is in its second position,

means for sequentially moving said valve member between said first andsaid second positions, and pumping means associated with said inlet andreturn openings and with said flow passage for continuously circulatingmolten plastic through said apparatus when said valve member is in bothits first and its second positions.

5. The structure of claim 4 in which said means comprises anair-operated piston, said piston being connected to said movable valvemember for moving said mem er between first and second positions.

6 In an apparatus having a pair of complementary mold sections formolding hollow products of a plastic capable of melting upon heating andof passing into a hardened state upon cooling, a valve assembly forC011- trolling the now of molten plastic and compressed air to said moldsections, said valve assembly comprising a valve casing having a boreextending therethrough and a valve member movable within said borebetween a first and a second position, said casing having a flow passagecommunicating with said here and being adapted to communicate with acavity defined by said mold sections, said valve member having endportions and an intermediate portion of reduced transverse dimensionsproviding an annular space Within said bore between said end porti0ns,lone of said end portions providing an air passage therethrough adaptedfor alignment with said flow passage of said casing when said member isin said second position, said casing having an inlet opening for theflow of molten plastic material into the annular space surrounding theintermediate portion of said valve member, said flow passage of saidcasing communicating with said annular space only when said valve memberis in said first posi tion, said casing also having a plastic-returnopening communicating with said annular space only when said valvemember is in said second position, whereby, when said valve member is insaid first position molten plastic material may be forced through saidinlet opening and into said flow passage of said casing and when saidvalve member is in said second position said molten plastic may returnto its source through said return opening and compressed air may flowthrough said member and into said flow passage, and means associatedwith said valve assembly for circuiating molten plastic continuouslythrough said apparatus when said valve member is in both its first andits second positions.

7. The structure of claim 6 in which said casing is provided with achamber therein, said casing also providing an inlet and outlet to saidchamber for the circulation of a heat-containing fluid therethrough,

8. T'ne structure of claim 6 in which piston means are provided forsequentially moving said valve member between said first and said secondposition within said bore.

References Cited in the file of this patent UNITED STATES PATENTS1,820,653 Ernst Aug. 25, 1931 2,782,801 Ludwig s Feb. 26, 1957 2,885,733Chupa May 12, 1959 2,991,506 Crandall July 11, 1961 FOREIGN PATENTS722,189 France Dec. 28, 1931 697,326 Great Britain Sept. 23, 1953405,386 Italy Mar. 26, 1941

